FIG. 8A and FIG. 8B show typical schematic structures of a group III nitride semiconductor luminescence element 41. FIG. 8A is a top view of the element, and FIG. 8B shows the cross section at A-A line of FIG. 8A. The group III nitride semiconductor luminescence element 41 is formed with a laminate (hereinafter, this may be referred as a “laminate semiconductor layer”) having a n-type layer 12, an active layer 13, and a p-type layer 14 on one surface side of a substrate 11; and having a mesa structure 15 at a part of the laminate semiconductor layer thereof is known. The mesa structure 15 is formed by forming the laminate semiconductor layer including the n-type layer 12, the active layer 13, and the p-type layer 14 on one surface side of the substrate 11, and then removing a part of the laminate structure by etching or so to expose a part of the n-type layer 12. A part having a plateau shape (also called as a mesa) including the active layer 13 and the p-type layer 14 is maintained; thereby the mesa structure 15 is formed (see the patent document 1). An n-electrode 16 is formed on the exposed surface of the n-type layer 12, and a p-electrode 17 is formed at the surface of the p-type layer 14.
For the group III nitride semiconductor luminescence element 41 having the mesa structure 15, when the driving voltage is applied to the p-electrode 17 on the p-type layer and the n-electrode 16 on the n-type layer, the current flows through the pathway having a low resistance (usually the shortest pathway) between the p-electrode and the n-electrode, thus the current runs by concentrating near the edge part of the mesa structure 15 (hereinafter, it may be called as a “mesa edge”) close to the n-electrode and the p-electrode. As a result, the current does not flow uniformly to the active layer 13, thus uneven luminescence occurs and causes the luminescence efficiency to decrease.
The patent document 2 discloses the ultraviolet semiconductor luminescence element wherein the high resistance layer having higher resistance than the p-type layer or p-electrode is formed on the surface of the p-type layer in a shape along the shape of p-type layer side at a side closer to the n-electrode. As disclosed in the patent document 2, when the high resistance layer is formed on the p-type layer close to the mesa edge, the current can be suppressed from concentrating near the mesa edge.
The patent document 3 discloses the semiconductor luminescence element wherein a trench is formed between the p-electrode and the n-electrode. By forming the trench, the length of the current pathway running between the p-electrode and the n-electrode is suppressed from varying; thereby the current is suppressed from concentrating to a particular part. However, in order to make the varying of the length of the current pathway sufficiently small, the depth of the trench must be deep.
Due to various designs of the recent devices, the luminescence element having various shapes and constitutions has been proposed, and also there are variety of mesa structures and designs of the electrode shapes. Thus, the art of forming the high resistance layer and trench as mentioned in the above will increase the steps for producing the luminescence element, and the production will be complicated, hence it has become difficult to correspond to the various mesa structures and electrode shapes in a timely manner.
Further particularly, the deep ultraviolet ray luminescence element having the luminescence peak wavelength of 200 to 350 nm has increased specific resistance of the n-type layer because Al composition is high in the n-type layer, thus the current tends to concentrate near the mesa edge, which tends to decrease the luminescence efficiency. Thus, the development of the luminescence element capable of suppressing the decrease of the luminescence efficiency which is caused by the current concentration is in demand.